HABITS OF YELLOW PERCH. 327 
The spawning season in Lake Wingra comes earlier than in Lake Mendota. This is 
due largely to the fact that the ice goes out sooner and the smaller volume of water 
warms up more rapidly. Figures 3 to 6 show that the period of activity associated with 
the migration of perch into shallow water for spawning came nearly a month earlier in 
Lake Wingra. In the spring of 1916 the ice left Lake Wingra March 20 and Lake 
Mendota April 8. The temperature just below the surface on April 18 was 10.6° C. in 
Lake Wingra and 4.6° C. in Lake Mendota. Our observations agree with those of 
Forbes and Richardson (1908), who state that the spawning of perch takes place in 
April and May, when the temperature of the water is 7 to 10° C.% Compared with other 
species of fishes and amphibians which lay eggs in the spring, the perch spawn rather 
early. During the spring of 1916 the following sequence was observed in Lake Mendota: 
April 12, the swamp-tree frog, Corophilus nigritus, was singing in the swamps along 
shore; April 20 to May 7, perch were spawning; May 2, the larve of the orl fly, Szalis inju- 
mata, were migrating on shore; May 12, suckers, Catostomus commersonit, were spawning ; 
May 30, crappies and dogfishes were frequenting bare spots alongshore; and June 19, 
crappiesin Lake Wingra werespawning. When most of the perch in Lake Mendota were 
spawning, the majority of those in Lake Wingra were already spent. In the autumn 
also the gonads of the perch in the smaller lake were noticeably earlier in reaching the 
large size characteristic of the cooler months, and this is again correlated with the earlier 
cooling of the lake. 
Perch come into shallow water alongshore to breed. The males precede the 
females and remain longer on the spawning grounds. This means that there are many 
more males than females in shallow water from the middle of April until the early 
part of May.?. For example, on April 28, 1916, a 1-inch mesh gill net, pulled from a depth of 
less than 3 m.,contained 380 perch, and all but four wereripe males (Table 26). Therewere 
three ripe females and one immature male. On May 2 and 12 there was still a great 
preponderance of males in the nets set in shallow water, but on later dates the sexes 
became more or less similarly distributed at all depths. The males evidently came 
inshore and remained during the entire spawning season; the females left deep water 
for only a short time to lay their eggs. Meek (1916, p. 281) records similar behavior 
for the plaice: ‘‘Results appear to show that the males appear first at the spawning 
ground and remain during the season, whereas the females depart shortly after the ova 
are shed.”” Abbott (1878) states that perch go in pairs to the spawning beds. In our 
gill-net catches a ripe female was often surrounded by several males. This indicates 
that a female may be attended by more than one male. 
Breeding instincts appear to dominate feeding instincts at the time of spawning. 
Table 22 shows that about 6 per cent of the individuals captured during the breeding 
season contained no food, and it was mostly the males that were empty. Another 
difference in feeding activities was noted between the sexes. The fishermen on Lake 
Mendota have stated on various occasions that they always caught more females than 
males when fishing in deep water through the ice with hook and line. The following 
observations support this view: December 29, 1916, 13 m., 40 females, o males; Decem- 
@ On May 7, 1920, at 4.25 p. m., the writer set two 4 by 7s gill nets, tied end to end, at a depth of 2.7 m. on the south shure 
of Lake Mendota. At 10.45 8. m. on May 8 the 1!4 inch mesh net contained a rock bass anda pickerel. The r-inch mesh net 
at 8.15 a. m. on May 8 had caught 921 ripe male perch, ro ripe female perch, 9 spent female perch, 4 female perch which had 
whitish eggs in their ovaries, and 1 mud puppy. ‘The food of the last consisted of crayfishes, 92; Physa heterostropha, 4; plant 
remains, 2; Leptocella larva and case, 1; perch eggs, 1. The water temperature (first figure in each set indicating depth in 
meters; second, degrees centigrade) was as follows: 0, 11; 1, 10.8; 3, 10.4; 4, 10; 5, 9-7; 6, 8.1; 7, 7-2; 8, 7.1; 10, 6.9; 13, 6.5; 15, 6.4; 
18, 6.1; 20, 5.8; 23.5, 5.6. 
